A known method for analyzing a blood flow in the heart uses images of the heart of a subject captured after a contrast medium has been administered to the subject.
Single photon emission computed tomography (SPECT) is a myocardium perfusion inspection that has been widely employed in medical practices for some time. The SPECT inspection has advantages in that it involves less contraindications, it is a well-established inspection method, and whole heart imaging is employed. Sufficient evidence has been found for further advantages of the SPECT inspection. More specifically, an incidence of cardiac events can be estimated in accordance with severity of myocardium ischemia detected by the SPECT inspection. In this context, a best outcome can be achieved by selecting a treatment policy in accordance with the severity. However, the SPECT inspection has disadvantages in that spatial resolution is insufficient, and it cannot be executed concurrently with coronary stenosis assessment.
Recently, there have been many reports on effectiveness of a magnetic resonance imaging (MRI) inspection for myocardium ischemia assessment. The MRI inspection has advantages such as no radiation exposure, less side effects from a contrast medium, and a high spatial resolution. Still, the MRI inspection has disadvantages such as long inspection time, variations in heart phases due to difference in a data collection time phase between slices, and contraindication such as pacemakers unsuitable for the MRI.
A stress myocardium perfusion computed tomography (CT) is a noninvasive stress myocardium perfusion inspection that has recently been reported to be effective. The inspection has a huge advantage over other modalities in that it can assess whether the subject suffers from myocardium ischemia, with coronary CT angiography concurrently conducted through highly accurate coronary artery morphology assessment. Up until recently, perfusion CT has mainly relied on single shot-examination involving imaging only in a single time phase under stress, and qualitative assessment has been performed on a static image. Actually, the imaging timing optimum for the myocardium perfusion assessment differs between cases, and it has been difficult to capture an image while measuring an imaging timing. Fortunately, recent development of imaging devices has enabled a quantitative assessment on the myocardium perfusion through analysis on a time density curve (TDC) obtained by a dynamic scan.
NPL 1 discusses a method of analyzing the TDC. The method includes: analyzing a time-series dynamic MRI images of the heart; and calculating an arrival time indicating a time at which a contrast medium has arrived at a predetermined myocardium region.
In clinical point of view, advancement of CT devices has led to remarkable improvement in spatial and temporal resolution in coronary CT inspections for the heart. Thus, the coronary CT inspection is widely used for medical diagnostics of circulatory organs, as a noninvasive inspection with the same diagnostic accuracy with coronary angiography (CAG). Furthermore, development of CT devices such as a plane detector CT, a high-resolution CT, and a dual-surface CT has made way for new image techniques such as subtraction imaging and dual energy imaging used in clinical practice. Thus, now the coronary CT inspection may be effective for the coronary stenosis assessment in cases deemed to have been difficult such as hyperdynamic, arrhythmia, and coronary artery calcification cases.
It has been widely known that even when a symptom of morphological coronary stenosis has been found, it does not necessarily mean that a symptom of functional myocardium ischemia has been found. Whether coronary stenosis lesion involves myocardium ischemia is an important factor for determining whether to perform revascularization treatment (such as catheter therapy or surgical therapy, for example). Unfortunately, in actual practice, whether to conduct therapeutic intervention on the coronary stenosis lesion, found by the coronary CT inspection, may be determined based on uncertain symptoms in some cases. More specifically, there might not be enough time or enough medical staff to perform a plurality of different inspections (the coronary stenosis assessment and the myocardium ischemia assessment) before the therapeutic intervention is conducted. This is because ischemic heart diseases are peculiar in that delay in the therapeutic intervention could be critical.